Oxidative hair dye colorants are essential elements in hair dyeing preparations for the permanent dyeing of human hair. The hair dyeing process is achieved, in general, by the reaction of certain developing compounds with certain coupling compounds in the presence of a suitable oxidizing agent or compound, such as hydrogen peroxide.
When oxidation dyes, such as those comprising primary intermediates and couplers are used in the dyeing of human hair, the procedure may involve the use of a two part system. In general, one part can be a lotion formulation which contains a variety of ingredients, including oxidation dye precursors (i.e., primary intermediates and coupling agents). The other part is a developer formulation containing a suitable oxidizing agent, e.g., hydrogen peroxide. Immediately prior to application to the hair, the two parts are mixed to form a thickened liquid solution, for example, a lotion or a gel. As a consequence of the oxidizing properties of the oxidizing agent, some of the natural melanin pigment of the hair may be bleached. The precursors in the thickened solution (e.g. lotion or gel) penetrate into the hair where the primary intermediates are oxidized and react with the coupling agents to produce the desired color. Such systems generally contain a proportion of organic solvents and surfactants and contain relatively high levels of dye precursors to produce the desired color.
In order for procedures using permanent oxidative dyes to work properly, a number of parameters and conditions are important to consider in the use of these dyes in admixture with couplers in hair color preparations for human hair. Among these are the final color and color intensity that are produced after application to the subject's hair; the wash fastness and the light fastness of the resulting dye; the resistance of the dye to perspiration; the resistance of the dye to various hair treatments, such as permanent wave, straightening, shampooing, conditioning and rubbing. In addition, the dye must have virtually no allergenicity or dermal or systemic toxicity.
p-Phenylenediamine plays a very important role in oxidative hair coloring because a majority of shades are obtained with dyes based on this dye. However, the hair coloring industry is searching for p-phenylenediamine alternatives possessing better allergenic profiles than p-phenylenediamine. As part of the solution, GB 2,239,265A describes that 2-(2-hydroxyethyl)-p-phenylenediamine can be used as a potential replacement for p-phenylenediamine. U.S. Pat. No. 5,538,516 also describes the use of 2-(hydroxyalkoxy)-p-phenylenediamine as a p-phenylenediamine substitute. European patent 634,163A lists more than 40 compounds of p-phenylenediamine derivatives. Among them, N-4-aminophenylmorpholine and N-4-aminophenylpiperidine were described. Morpholine and piperidine derivatives are examples of heterocyclic compounds. No example of pyrrolidine was found in the list. However, these compounds are not good primary intermediates because the energy required for the formation of the oxidized forms of the piperidine and morpholine derivative is higher than for the open chain compound such as 4-amino-N,N-diethylaniline (R. L. Bent, J. C. Desslock, F. C. Duennebier, D. W. Fassett, D. B. Glass, T. H. James, D. B. Julian, W. R. Ruby, J. M. Snell, J. H. Sterner, J. R. Thirtle, P. W. Vittum and A. Weissberger, J. Am. Chem. Soc. 1951, 73, 1300). It was also reported in this paper that formation of the oxidized compound is even more favorable for 1-(4-aminophenyl) pyrrolidine than for the 4-aminodialkylanilines with open alkyl groups such as 4-amino-N,N-diethylaniline. Although 1-(4-aminophenyl)pyrrolidine has a good potential as a primary intermediate, it was found to exhibit a strong allergenic activity. Because of adverse biological activity and various limitations, there is need for developing pyrrolidine derivatives which can be used as p-phenylenediamine alternatives.
In R. L. Bent, J. C. Dessloch, F. C. Duennbier, D. W. Fassett, D. B. Glass, T. H. James, D. B. Julian, W. R. Ruby, J. M. Snell, J. H. Sterner, J. R. Thirtle, P. W. Vitt, A. Weissberger, Chemical constitution, Electrochemical, Photographic and allergenic properties of p-amino-N-dialkyanilines, J. Am. Chem. Soc. 1951, 73, 1300, a total of 60 of 4-amino-N, N-dialkylanilines were studied on allergenic properties. 1-(4-Aminophenyl)pyrrolidine was one of them mentioned in the studies.